The metal plate marked "1 SAT" indicates the next collection (1st collection of Saturday). In fact "NEXT COLLECTION" is cast into the box itself to the left of the plate. The full schedule is listed in the lower 50% of the notice.

I now see that the notice continues "This letter box is privately owned." I guess you have to trust the owner to enter your letters into the "real" Royal Mail.
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The metal plate marked "1 SAT" indicates the next collection (1st collection of Saturday). In fact "NEXT COLLECTION" is cast into the box itself to the left of the plate. The full schedule is listed in the lower 50% of the notice.

I now see that the notice continues "This letter box is privately owned." I guess you have to trust the owner to enter your letters into the "real" Royal Mail.